@article{DE_1976_12_11_a26,
     author = {L. A. Cherkas and G. M. Buldyk},
     title = {Integral curves of a certain class of differential equations that have a center},
     journal = {Differencialʹnye uravneni\^a},
     pages = {2102--2104},
     publisher = {mathdoc},
     volume = {12},
     number = {11},
     year = {1976},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/DE_1976_12_11_a26/}
}